1. Field of the Invention
The present invention relates in general to a laminar structure and a hose formed of the laminar structure. More particularly, the invention is concerned with such a laminar structure which exhibits excellent adhesiveness or adhesive strength between a first layer formed of a fluoro rubber or a fluoro resin and a second layer formed of an epichlorohydrin rubber. In particular, the invention relates to a hose, above all, a fuel hose, having such a laminar structure.
2. Discussion of the Related Art
A laminar structure having a plurality of layers which are laminated on one another is conventionally used for various applications. For instance, there is known a laminar structure consisting at least of a first layer formed of a fluoro rubber or a fluoro resin, and a second layer which is laminated in contact with the first layer and which is formed of an epichlorohydrin rubber. Such a laminar structure is used as a hose by utilizing the characteristics of the materials which provide the individual layers of the laminar structure. In particular, the laminar structure is used as a fuel hose wherein the first layer serves as an innermost layer of the hose, by taking advantage of excellent fuel impermeability of the fluoro rubber or fluoro resin which provides the first layer.
For providing the laminar structure as described above, it is required to bond the first layer of the fluoro rubber or fluoro resin and the second layer of the epichlorohydrin rubber to each other. However, it is known that the fluoro rubber or fluoro resin has low adhesiveness with respect to other materials. In view of this, there have been made various research to provide an improved bonding technique which assures sufficient bonding between the fluoro rubber or the fluoro resin and the epichlorohydrin rubber. However, the conventionally proposed bonding techniques put a great emphasis on the improvement of the bonding between the first layer of the fluoro rubber or fluoro resin and the second layer of the epichlorohydrin rubber, so that the epichlorohydrin rubber suffers from compression set and reduced resistance to sour gasoline, and the storage stability of unvulcanized rubber is deteriorated.
When the fluoro rubber or fluoro resin and the epichlorohydrin rubber are bonded by vulcanization, the vulcanization system of the epichlorohydrin rubber generally includes ethylenethiourea as a vulcanizing agent and a lead compound such as minium as an acid receptive agent. In addition, calcium hydroxide, a salt of 1,8-diazabicyclo(5,4,0)undecene-7 and/or onium salt are added to the vulcanization system, to thereby improve the adhesive strength between the fluoro rubber or fluoro resin and the epichlorohydrin rubber. However, in view of the recently increasing worldwide demand for safety, it is desirable to regulate disposal and use of the lead compound. Accordingly, there is an urgent demand for development of an alternative vulcanization system which does not use the lead compound.
As a result of an extensive study by the inventors of the present invention so as to find the alternative vulcanization system which does not use the lead compound, it has been found that a specific vulcanization system significantly improves the adhesive strength between the fluoro rubber or fluoro resin and the epichlorohydrin rubber, permits the epichlorohydrin rubber to exhibit excellent characteristics in terms of compression set, and assures excellent sour gasoline resistance.